You wont give a link to the theme on the web so I cant look at it. I cant look on your localhost. You still havent answered the question of why you want to use the bootstrap modal. You haven't said if you have tried a custom build. You havent confirmed if bootstrap is loading on your localhost.
Not really anything to listen to
I actually do want to try and help you, but it is difficult.
Looking at that screenshot - it might be the MyBB modal - its quite hard to tell the two apart from a screenshot - the live site would be better.